1. Field of the Invention
The present invention relates to a wiring circuit substrate used for mounting electronic devices, such as integrated circuits (ICs) and large scale integrated circuits (LSI circuits). Particularly, the invention relates to a wiring circuit substrate that allows high-density mounting to be implemented.
Furthermore, the present invention relates to a manufacturing method for the aforementioned wiring circuit substrate.
2. Description of the Related Art
FIGS. 54A to 54F and 55A to 55C are used to describe a conventional example of a high-density-mounting wiring circuit substrate. These figures are cross-sectional views illustrating a manufacturing method for the conventional wiring circuit substrate in the order of steps (A) to (I) described below.
Step (A)
First of all, as shown in FIG. 54A, a base 1 is prepared. The base 1 is made of an insulating sheet having a thickness of 25 to 100 μm. In the base 1, interlayer-connecting openings 2 are formed by using a punching machine or a drill or by performing laser processing.
Step (B)
Subsequently, as shown in FIG. 54B, conductive paste 3 (made of a main material, for example, such as silver or copper) is filled into the openings 2 by using a printing method for example. Thereby, the insulating base 1 is arranged to be a semi-cured sheet A in which the conductive paste 3 is filled into the openings 2.
Step (C) and Step (D)
Subsequently, as shown in FIG. 54C, metal foils 4 made of, for example, copper, are individually arranged over two faces of the sheet A. Then, as shown in FIG. 54D, the metal foils 4 are overlaid by using a pressing/heating press. Thereby, a multilayer body is formed such that the metal foils 4 are formed on the two faces, an insulating sheet is provided therebetween, and the metal foils 4 on the two faces are electrically connected to each other via the conductive paste 3 in the openings 2.
Step (E)
Subsequently, resist films 5 are formed on the metal foils 4. The resist films 5 have the same pattern as that of conductor circuits that will be formed. FIG. 54E shows a state after the resist films 5 are formed.
Step (F)
Subsequently, using the aforementioned resist films 5 as masks, etching is performed for the aforementioned metal foils 4, thereby forming conductor circuits 6, as shown in FIG. 54F. According to the above, layers are separated and arranged on the two faces via the insulating sheet (base) 1, and a multilayer body B having the conductor circuits 6 interlayer-connected to each other via the conductive paste 3 in the opening 2 is formed.
Step (G)
Subsequently, as shown in FIG. 55A, on individual two faces of the aforementioned multilayer body B, insulating sheets 1a having openings 2 filled with conductive paste 3 and metal foils 4a are overlapped with each other. Thereafter, these component members are stacked with each other by using a press, and a multilayer body C is thereby formed.
Step (H)
Subsequently, as shown in FIG. 55B, resist films 5 are selectively formed on the metal foils 4a on two faces of the multilayer body C.
Step (I)
Subsequently using the resist films 5 as masks, etching is selectively performed for the metal foils 4a, thereby performing patterning therefor to form wiring films 6a, as shown in FIG. 55C. Thereby, a wiring circuit substrate 7 having four layers of the conductor circuits 6 and 6a are formed.
FIGS. 56A to 56G are used to explain another conventional example of a high-density-mounting wiring circuit substrate. These figures are cross-sectional views illustrating a manufacturing method for the conventional wiring circuit substrate in the order of steps (A) to (G) described below.
Step (A)
For example, as shown in FIG. 56A, a metal foil 10 (having a thickness of, for example, 18 μm) made of a copper material is prepared. Then, on the metal foil 10, conductive protrusions 11 are formed by a printing method via conductive paste (made of a main material such as a silver or copper material) and a metal plate, and then, are heated and cured. The protrusions 11 are thus formed so as to have thicknesses, for example, ranging from 100 to 300 μm.
Step (B)
Subsequently, as shown in FIG. 56B, an insulating adhesive sheet 12 is adhered onto the face on which the protrusions 11 of the aforementioned metal foil 10 are formed. For the adhesive sheet 12, an adhesive sheet having a thickness smaller than the thicknesses of the protrusions 11 is used. Thereby, the top of each of the protrusions 11 protrudes from the surface of the adhesive sheet 12. A multilayer body A is produced that has a configuration in which the protrusions 11 are formed on the metal foil 10 and the adhesive sheet 12 is adhered onto the surface of the metal foil 10 in a state of allowing the top of each the protrusions 11 to protrude therefrom.
Step (C) and Step (D)
Subsequently, as shown FIG. 56C, a metal foil 13 similar to the aforementioned metal foil 10 is arranged over the surface of the adhesive sheet 12, then, as shown in FIG. 56D, the metal foil 13 is overlaid on the adhesive sheet 12 and the protrusions 11 according to a heating-pressing method. Thereby, a multilayer body B is produced.
Step (E)
Subsequently, for example, resist films for which patterning is performed are formed on the metal foils 10 and 13 individually formed on two faces of the multilayer body B. Then, etching is performed for the metal foils 10 and 13 by using the resist films as masks, thereby forming conductor circuits 14 and 15. FIG. 56E shows a configuration where the resist films used as masks are removed after the conductor circuits 14 and 15 are formed.
Step (F)
Subsequently, two multilayer bodies a are prepared. Each of the multilayer body (a) is formed by the same method as that for the multilayer body (A) shown in FIG. 48B. As shown in FIG. 56F, the two multilayer bodies (a) are individually arranged over two faces of the aforementioned multilayer body (B).
Step (G)
The aforementioned multilayer body (B) is sandwiched by the multilayer bodies (a), and the integrated body is pressed from the sides of two faces thereof according to the aforementioned heating-pressing method. Thereby, a wiring circuit substrate 16 as shown in FIG. 56G is produced.
Subsequently, a still another conventional technique will be explained. FIGS. 57A to 57E and 58A to 58D show a production process of still another wiring circuit substrate.
Step (A)
As shown in FIG. 57A, a copper-plated laminated plate 400a is prepared for forming a hole 400b for connection therein by drilling or laser processing. The numeral 400c is an insulating sheet to serve as the base member for the laminated plate 400a, and 400d, 400d are copper foils formed on both sides of the insulating sheet 400c. 
Step (B)
Subsequently, as shown in FIG. 57B, a copper plating layer 400e is formed on the entire surface by an electroless plating process and a subsequent electrolytic plating process.
Step (C)
Subsequently, as shown in FIG. 57C, the hole 400b is filled with an insulating resin 400f, such as an epoxy.
Step (D)
Subsequently, as shown in FIG. 57D, both sides of the laminated plate 400a is smoothed by mechanical polishing. Thereafter, another copper plating layer 400g is formed by an electroless plating process and a subsequent electrolytic plating process. Accordingly, the insulating resin 400f filling up the hole 400b is covered by the copper plating layer 400g. 
Step (E)
Subsequently, as shown in FIG. 57E, a wiring film 400h is formed by patterning the copper plating layers 400g, 400d, 400e on both sides of the laminated plate 400a. The etching operation is executed by applying a resist film, exposing and developing the same so as to form a mask pattern, and selective etching with the mask pattern used as the mask. After the etching, the resist film is eliminated.
Step (F)
Subsequently, as shown in FIG. 58A, an insulating resin 400i, 400i is coated on both sides of the laminated plate 400a. Thereafter, a hole 400j to be a through hole is formed in the insulating resin 400i by a laser beam. At the time, the residual resin adhered on the surface of the copper foil 400d should be eliminated by using a washing liquid.
Step (G)
Subsequently, as shown in FIG. 58B, a copper plating layer 400k is formed on both sides of the laminated plate 400a by an electroless plating process and an electrolytic plating process.
Step (H)
Subsequently, as shown in FIG. 58C, a circuit 400l is formed by patterning the copper plating layers 400k on both sides of the laminated plate 400a. The etching operation is executed by selective etching with a mask formed by patterning a resist film by exposing and developing used as the mask. Thereafter, the resist film used as the mask is eliminated.
Step (I)
Subsequently, as shown in FIG. 58D, both sides of the laminated plate 400a are covered selectively by a solder resist 400m. Accordingly a wiring circuit substrate 400n is completed.
However, the conventional example shown in FIGS. 54 and 55 arises problems as described the followings. First, the openings 2 in the insulating sheet 1 are filled with the conductive paste 3 made of a main material such as expensive silver material and are used for interlayer connection. This arises a problem of increasing costs. Particularly, since arrangement density of the openings 2 is required to be increased according to an increasing demand for high-density mounting, the increase in costs becomes noticeable so as not to be ignored.
Second, when the conductive paste 3 is filled into the openings 2, the conductive material is adhered to portions other than the openings 2, although the amount thereof is very small. This arises a problem of reducing the insulation resistance, particularly in a high-humidity environment.
Third, when press-overlaying is performed after the openings 2 are formed in the insulating sheet 1, the insulating sheet 1 is forced to horizontally extend. Thereby, positional deviation of the openings 2 occurs. Even by performing correction thereof and making openings, the correction is not effective in the high-density pattern. The positional deviation of the openings 2 causes defective interlayer connection, thereby arising serious problems, which cannot be ignored. Particularly, the problem is critical for the high-density-mounting wiring circuit substrate.
Fourth, the reliability of the connection between the metal foils 4 made of a copper material and the conductive paste 3 is insufficient. The conductive paste 3 filled into the openings 2 removes a solvent component so as to be a semi-cured state. The semi-cured conductive paste shrinks because of removal of the solvent component and the like, thereby reducing the volume of its own. In addition, in most cases, upper and lower faces of the conductive paste 3 become in a concave state. As a result, defective connection is apt to be caused between the metal foils 4, thereby arising a problem of reducing the reliability and the yield.
Subsequently, the conventional example shown in FIGS. 56A to 56G also arises problems as described the followings. First, using the protrusions 11 formed of the conductive paste also arises the problem of increasing costs.
Second, since a screen-printing method is used to form the protrusions 11 with the conductive paste, increase in the thickness thereof is restricted. Therefore, in most cases, screen-printing operations must be repeatedly performed to form the protrusions 11.
When the number of the printing operations is increased, the positional deviation of the protrusions 11 is apt to occur, and deformation of the protrusions 11 is thereby apt to occur. This develops a problem of reducing the reliability of the connections between the protrusions 11 and the metal foils 4. In addition, positioning operation for the screen-printing is very difficult and requires high-level skills, thereby causing a problem of requiring relatively long processing time.
These problems become increasingly apparent in proportion to reduction in the diameter of each of the protrusions 11. For example, for protrusions each having a diameter of 0.3 mm, two printing operations must be performed; and for protrusions each having a diameter of 0.2 mm, four printing operations must be performed. This is heavy work and disturbs improvement in the productivity, remaining problems to be solved for the provision of high-density wiring circuit substrates.
Third, still another problem arises in that heights of the protrusions 11 are likely varied. In specific, in the screen-printing method, since it is difficult to uniform thicknesses of films, heights of the protrusions 11 formed thereby are also likely to be variable. The variation in the thickness likely causes the connection between the metal foil 13 and the protrusions 11 to be defective. This results in arising a problem of reducing the yield and the reliability.
Fourth, in the manufacturing stage, the metal foil 10 basing the wiring circuit substrate is as thin as, for example, 18 μm. Therefore, in the screen-printing sufficient care must be taken to prevent it from being wrinkled, deformed, and bent on the metal foil 13 side. Even a very minor operation problem could reduce the yield. This develops to the problem of increasing costs, which should not be neglected. Conversely, increasing the thickness of the metal foil 10 so as to obtain a strong base also causes a problem of disturbing the conductor circuits to be finely patterned.
One of problems common to the described conventional examples is that there are restrictions in making the high-density arrangement, that is, in the arrangement of fine interlayer connection. In the case of one example, the printing operation is difficult because of the reduction in the diameters of the openings and difficulty in filling the conductive paste into the openings. In the case of another conventional example, the difficulty in the printing operation increases in proportion to the reduction in the diameters in bump printing. Thus, according to the conventional technology, an opening having a diameter smaller than 200 μm cannot be produced.
In addition, since the strength of the connection between the conductive paste and the copper foil is low, an excessively large area is required for the connection.
Next, the wiring circuit substrate shown in FIGS. 57A to 57E and 58A to 58D also involves problems.
A first problem is a poor adhesion property between the surface of the insulating resin 400f for filling the hole 400b and the copper plating layer 400g so as to easily generate adhesion failure.
Particularly at the time of mounting, in the case various members are connected with the area, there is a risk of generating fall-off.
Moreover, in order to solve the problem, the wiring circuit substrate needs to be designed so as not to superimpose the connecting points of the various members and the hole 400b formation area. Therefore, it gives the limitation in designing so as to be a cause for prohibiting a high density of the wiring circuit substrate.
A second problem is deflection of the surface of the copper plating layer 400k in the area with the hole 400j because the copper plating layer 400k is formed in the area with the hole 400j. 
Therefore, a wiring layer cannot be formed further on the copper plating layer 400k, and thus a multi-layer structure cannot be provided.
A third problem is the inability of ensuring a sufficient film thickness in the area with the hole 400j because the copper plating layer 400k is formed in the area.
That is, the copper plating layer 400k is formed by an electroless plating process and a subsequent electrolytic plating process. The film formation rate in the electroless plating process is low. Furthermore, the film thickness irregularity can easily be generated in the electrolytic plating process in relation to the electrolytic distribution. Therefore, even in a level difference part for forming the hole 400j, a film is formed with a thin film thickness so that a sufficient film thickness cannot be ensured. This point has prohibited realization of minuteness of the wiring circuit substrate.